Non-rigid vinyl chloride resins have advantageous properties including flexibility, transparency and toughness, and some of the properties such as flexibility can be controlled at will by varying the amount of a plasticizer added. For these reasons, they are widely used in various applications including films, sheets, and extrusion molded articles. However, adhesion of non-rigid vinyl chloride resins is not necessarily easy. While many proposals have been made on adhesives for non-rigid vinyl chloride resins, none of them has been found completely satisfactory. Many of the prior art adhesives for non-rigid vinyl chloride resins comprises a solution of an adhesive ingredient such as chloroprene rubbers, nitrile rubbers and polyesters. Because of the use of a solvent, solution type adhesives have posed problems of pollution of working environment, need of a step of drying the solvent and expensive costs involved.
There have been already known solvent free adhesives which can realize thermal adhesion without suffering from the above-mentioned problems and which can be used in adhesion of non-rigid vinyl chloride resins. Such known adhesives include, for example, those based on copolymers of ethylene and vinyl acetate having vinyl chloride grafed (Japanese Patent Laid-open Publication No, 57-167,362), carboxylated copolymers of ethylene and vinyl acetate (Japanese Patent Laid-open Publication No, 59-52,174) and copolymers of ethylene, vinyl acetate and carbon monoxide (Japanese Patent Laid-open Publication No, 57-165,427). However, these copolymers have relatively low melting points, and therefore, when an adherend coated with an adhesive comprising the copolymer mentioned above is exposed to a hot atmosphere, adhesive failure frequently takes place even with a slight shearing.
In view of the state of the art, as discussed above, we have studied to seek for an adhesive which is excellent in heat resistance and capable of realizing thermal adhesion. As a result we have found that a novel graft copolymer comprising a stock copolymer (A) of at least one monomer selected from esters of unsaturated carboxylic acids and vinyl esters (a), ethylene (b) and carbon monoxide (c), and a polyamide oligomer having a primary amino group at one end of its molecule (B) grafted on said stock copolymer, is excellent in heat resistance, can realize thermal adhesion and, moreover, has other desirable properties. The invention is based on these findings.